The present invention relates to radar warning receivers for detecting and analyzing radar signals. The invention is particularly applicable to radar warning receivers for installation into military aircraft to provide self-protection to the aircraft against radar guided threats, such as air-to-air or surface-to-air missiles, and the invention is therefore described below with respect to this application.
Radar warning receivers provided on military aircraft must not only detect the radar signals but must also determine a number of their parameters, e.g., direction, frequency, amplitude, time of arrival, and pulse width. These parameters must be measured quickly in order to enable the aircraft to counter the threat by avoiding it or by activating various electronic counter-measures. For this purpose, an ideal radar warning receiver must have a number of characteristics including the following: automatic operation; high sensitivity, to detect threats while still at a distant range; high reliability, to provide high probability of intercept and low probability of false alarm; good coverage, to have a large frequency band width to cover all threats, good angular coverage to protect the aircraft from every direction, and large dynamic range to protect against weak or strong signals; fast operation, to provide readiness for the appearance of a new threat; accuracy, to provide accurate identification and direction finding; protection against spurious and other signals, to enable full performance in a dense-signal environment; simple to install in different aircraft, to integrate with other systems, and to maintain; and low cost construction susceptible to volume production.
The emergence of new radar types and technologies poses a host of problems to the radar warning receiver which current systems find difficulty in meeting. Thus, the newly developed PD (pulse doppler), SPSP (spread spectrum), TWS (track while scan), FA (frequency agility), and PRI (pulse repetition interval) agility radar systems impose new and harsh requirements for the modern radar warning receiver.
There are many basic receiver types in use today, but all have their drawbacks: Thus, the crystal video receiver (CVR) cannot measure frequency, is of low sensitivity, and cannot operate in dense environments; the instantaneous frequency monitor (IFM), which is an enhancement to the CVR, provides it with frequency measurement capability, but it is of relatively low sensitivity and of little protection for operating in a dense environment. The superheterodyne (or superhet) receiver (SHR) does achieve the required sensitivity and protection, but its low probability of intercept, and its inability to handle frequency-agile radars, make it outdated. The channelized receiver (CR) combines high sensitivity with high probability of intercept, and is well protected, but its complexity and high cost make it an unlikely choice, especially when it needs to be multiplied to enable direction-finding.
Many existing radar warning receivers employ a combination of two or more of the foregoing receiver types in order to compensate for the shortcomings of each type; but such combinations cannot fully complement each other, and the total resulted performance is not the best of each. In addition, in order to perform the instantaneous direction finding (IDF) function, several identical receivers are necessary to measure the same signal simultaneously. Thus, many radar warning receiver systems include a plurality of crystal video receivers for the IDF function because of the simplicity and low cost of this receiver, but the IDF parameter, which is probably the most important parameter, is thereby sacrificed with respect to weak signals, and such combination systems are therefore quickly degraded in dense signal environments.